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    <style>
        * {
            color: blue;
        }
        
        ul li {
            color: red;
        }
        
        .box {
            color: green;
        }
        
        #box1 {
            color: pink;
        }
    </style>
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    <ul>
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            云课堂
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<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=
    , initial-scale=1.0">
    <title>Document</title>
    <style>
        .box div {
            width: 100px;
            height: 100px;
            border: 2px solid red;
            margin: 50px 0;
            box-sizing: border-box;
        }

        .box div:nth-child(2):hover {
            color: red;
            background-color: green;
        }
    </style>
</head>

<body>
<div class="box">
    <div>苹果</div>
    <div>橙子</div>
    <div>香蕉</div>
</div>
</body>

</html>